(core) Add 'user' variable to trigger formulas

Summary:
The 'user' variable has a similar API to the one from access rules: it
contains properties about a user, such as their full name and email
address, as well as optional, user-defined attributes that are populated
via user attribute tables.

Test Plan: Python unit tests.

Reviewers: alexmojaki, paulfitz, dsagal

Reviewed By: alexmojaki, dsagal

Subscribers: paulfitz, dsagal, alexmojaki

Differential Revision: https://phab.getgrist.com/D2898

sandbox/grist/user.py

@@ -0,0 +1,62 @@
+"""
+This module contains a class for creating a User containing
+basic user info and optional, user-defined attributes that reference
+user attribute tables.
+
+A User has the same API as the 'user' variable from
+access rules. Currently, its primary purpose is to expose
+user info to trigger formulas, so that they can reference info
+about the current user.
+
+The 'data' parameter represents a dictionary containing at least
+the following fields:
+
+ - Access: string or None
+ - UserID: integer or None
+ - Email: string or None
+ - Name: string or None
+ - Origin: string or None
+ - LinkKey: dictionary
+
+Additional keys may be included, which may have a value that is
+either None or of type tuple with the following shape:
+
+ [table_id, row_id]
+
+The first element is the id (name) of the user attribute table, and the
+second element is the id of the row that matched based on the
+user attribute definition.
+
+See 'GranularAccess.ts' for the Node equivalent that
+serializes the user information found in 'data'.
+"""
+import six
+
+class User(object):
+  """
+  User containing user info and optional attributes.
+
+  Setting 'is_sample' will substitute user attributes with
+  typed equivalents, for use by autocompletion.
+  """
+  def __init__(self, data, tables, is_sample=False):
+    for attr in ('Access', 'UserID', 'Email', 'Name', 'Origin'):
+      setattr(self, attr, data[attr])
+
+    self.LinkKey = LinkKey(data['LinkKey'])
+
+    for name, value in six.iteritems(data):
+      if hasattr(self, name) or not value:
+        continue
+      table_name, row_id = value
+      table = tables.get(table_name)
+      if not table:
+        continue
+      # TODO: Investigate use of __dir__ in Record for type information
+      record = table.sample_record if is_sample else table.get_record(row_id)
+      setattr(self, name, record)
+
+class LinkKey(object):
+  def __init__(self, data):
+    for name, value in six.iteritems(data):
+      setattr(self, name, value)